The rapid evolution of lungfish durophagy

Innovations relating to the consumption of hard prey are implicated in ecological shifts in marine ecosystems as early as the mid-Paleozoic. Lungfishes represent the first and longest-ranging lineage of durophagous vertebrates, but how and when the various feeding specializations of this group arose remain unclear. Two exceptionally preserved fossils of the Early Devonian lobe-finned fish Youngolepis reveal the origin of the specialized lungfish feeding mechanism. Youngolepis has a radically restructured palate, reorienting jaw muscles for optimal force transition, coupled with radiating entopterygoid tooth rows like those of lungfish toothplates. This triturating surface occurs in conjunction with marginal dentition and blunt coronoid fangs, suggesting a role in crushing rather than piercing prey. Bayesian tip-dating analyses incorporating these morphological data indicate that the complete suite of lungfish feeding specializations may have arisen in as little as 7 million years, representing one of the most striking episodes of innovation during the initial evolutionary radiations of bony fishes.

Time-calibrated phylogeny (constrained with strict consensus topology from parsimony analyses) obtained using IGR emphasizing relationships among Palaeozoic Dipnomorpha. The node ages are the posterior medians, with blue bars for each node representing 95% HPD intervals of age estimates. The color of the branch represents the mean relative clock rate along that branch. Supplementary Fig. 5 Time-calibrated phylogeny (no topological constraint) obtained using IGR emphasizing relationships among Palaeozoic Dipnomorpha. The node ages are the posterior medians, with blue bars for each node representing 95% HPD intervals of age estimates. The color of the branch represents the mean relative clock rate along that branch. Supplementary Fig. 6 IGR relative rates of phenotypic evolution for all dipnomorphs more closely related to crown lungfishes than to Porolepiformes. Partitioned analyses were performed with a topological constraint matching the strict consensus parsimony solution (as in Supplementary Fig. 4).
Supplementary Fig. 7 IGR relative rates of phenotypic evolution for all dipnomorphs more closely related to crown lungfishes than to Porolepiformes. Unpartitioned analyses with no constraint (as in Supplementary Fig. 5).
Supplementary Fig. 8 IGR evolutionary rate of characters associated with the feeding apparatus. The node ages are the posterior medians, with blue bars for each node representing 95% HPD intervals of age estimates. The color of the branch represents the mean relative clock rate at that branch. Partitioned analyses were performed with a topological constraint matching the strict consensus parsimony solution (as in Supplementary Fig. 4).
Supplementary Fig. 9 IGR evolutionary rate of characters not associated with the feeding apparatus. The node ages are the posterior medians, with blue bars for each node representing 95% HPD intervals of age estimates. The color of the branch represents the mean relative clock rate at that branch. Partitioned analyses were performed with a topological constraint matching the strict consensus parsimony solution (as in Supplementary Fig. 4).

Supplementary Fig. 10
Time-calibrated phylogeny (constrained with strict consensus topology from parsimony analyses) obtained using ILN emphasizing relationships among Palaeozoic Dipnomorpha. The node ages are the posterior medians, with blue bars for each node representing 95% HPD intervals of age estimates. The color of the branch represents the mean relative clock rate along that branch. Supplementary Fig. 11 Time-calibrated phylogeny (no topological constraint) obtained using ILN emphasizing relationships among Palaeozoic Dipnomorpha. The node ages are the posterior medians, with blue bars for each node representing 95% HPD intervals of age estimates. The color of the branch represents the mean relative clock rate along that branch. Fig. 12 ILN relative rates of phenotypic evolution for all dipnomorphs more closely related to crown lungfishes than to Porolepiformes. Partitioned analyses were performed with a topological constraint matching the strict consensus parsimony solution (as in Supplementary Fig.  10). Fig. 13 ILN relative rates of phenotypic evolution for all dipnomorphs more closely related to crown lungfishes than to Porolepiformes. Partitioned analyses were performed with no constraint (as in Supplementary Fig. 11).

Supplementary
Supplementary Fig. 14 ILN evolutionary rate of characters associated with the feeding apparatus. The node ages are the posterior medians, with blue bars for each node representing 95% HPD intervals of age estimates. The color of the branch represents the mean relative clock rate at that branch. Partitioned analyses were performed with a topological constraint matching the strict consensus parsimony solution (as in Supplementary Fig. 10). Fig. 15 ILN evolutionary rate of characters not associated with the feeding apparatus. The node ages are the posterior medians, with blue bars for each node representing 95% HPD intervals of age estimates. The color of the branch represents the mean relative clock rate at that branch. Partitioned analyses were performed with a topological constraint matching the strict consensus parsimony solution (as in Supplementary Fig. 10). Fig. 16 ILN evolutionary rate of characters associated with the feeding apparatus. The node ages are the posterior medians, with blue bars for each node representing 95% HPD intervals of age estimates. The color of the branch represents the mean relative clock rate at that branch. Partitioned analyses were performed with no topological constraint (as in Supplementary  Fig. 11). Fig. 17 ILN evolutionary rate of characters not associated with the feeding apparatus. The node ages are the posterior medians, with blue bars for each node representing 95% HPD intervals of age estimates. The color of the branch represents the mean relative clock rate at that branch. Partitioned analyses were performed with no topological constraint (as in Supplementary  Fig. 11). Fig. 18 Life reconstruction of Youngolepis praecursor and the associated biota. Art credit: Brian Choo. Glyptolepis from '0' to '-' Psarolepis from '0' to '-' 29.